1. Field of the Invention
This application is the national phase under 35 U.S.C. xc2xa7 371 of PCT International Application No. PCT/SE98/02411 which has an International filing date of Dec. 21, 1998, which designated the United States of America.
The present invention relates to an air treatment unit for treatment of an air stream flowing in a substantially horizontal direction and being blown through the unit from an inlet side to an outlet side, comprising at least one pad having an inlet surface, an outlet surface and a multitude of narrow air-flow channels extending from said inlet surface to said outlet surface, the walls of said channels being formed by corrugated sheets of a stiff material, said sheets being positioned and fixed generally in mutually parallel, substantially vertical planes next to each other in such a way that the channels formed by the corrugations of any two adjacent sheets extend in two different directions from said inlet surface to said outlet surface.
2. Description of Background Art
Such air treatment units are being frequently used today, in particular in order to humidify and cool the air stream while the pad is being drained with water. See, e.g., the instruction manual xe2x80x9cCELdek/GLASdek Contact material for evaporative cooling/humidificationxe2x80x9d issued by Munters Component AB 1993. Then, the water is evaporated and the air will thereby exchange sensible heat for latent heat. Preferably, the corrugated sheets forming the pad are impregnated with a wetting agent, so that the total surface area of the channel walls are constantly wet so as to secure an effective evaporation. The stiff material of the corrugated sheets may be a cellulose material, a glass fibre material, a synthetic fibre material or a plastic material or even an aluminium alloy provided with a hygroscopic surface layer. The corrugated sheets are positioned with the corrugations oriented in alternate directions, preferably being repeated for every second sheet, so that the channels formed by the corrugations are directed in different directions in adjacent or neighbouring sheets. At the time of manufacture, the sheets are glued together at the points where the corrugations cross each other, so as to form a rigid and stable unit. Normally, at the edge portions, the pad formed by the corrugated sheets can be firmly held in a frame, e.g. of stainless steel, aluminium or some other rigid, incombustible and non-corrosive material.
The pad can also be used as a droplet separator to be placed downstream a cooling pad or somewhere else in an air treatment unit or system where the air stream has a high velocity and contains water droplets. Since the channels in the pad stand at an angle in relation to the inlet flow direction of the airstream, the water droplets will hit the walls of the channels and be absorbed by the wet walls thereof.
The cooling or separator pads described above, in particular those manufactured and marketed by Munters, under the registered trademark CELdek and GLASdek, have proven to operate efficiently and reliably with long life in cooling and ventilation systems in buildings for public use, offices, industry, agriculture and livestock buildings. The last-mentioned application has become very important, in particular for raising animals and birds, especially chickens in large numbers. The pads are also being used in gas turbine inlets.
Thus, this kind of air treatment units with pads of corrugated sheets have become commercially very important, and there is a constant demand for further improvement. Accordingly, the main object of the present invention is to provide an air treatment unit with higher efficiency, increased strength and generally improved performance. A further, specific object is to provide an improved pad which enables a higher air stream velocity and a higher cooling and humidification efficiency.
These objects are achieved for an air treatment unit wherein, at least in a central, major region of the pad, said mutually parallel planes of said corrugated sheets are oriented obliquely relative to a substantially horizontal direction being normal to said inlet surface, whereby said air-flow channels extend obliquely not only in said two directions in said mutually parallel planes, but also obliquely sideways in a third direction as seen in said substantially horizontal, normal direction, as a consequence of said oblique orientation of said mutually parallel planes. In this way, for a given thickness of a pad, the air stream will be forced to travel a longer distance in the channel from the inlet surface to the outlet surface of the pad, whereby the evaporative process will be enhanced. Of course, there will also be an increased pressure drop caused by the extra deflection of the air stream. However, it has turned out that the net effect is a significant improvement of the cooling and humidifying capacity of the pad (for a given volume or thickness) and a greatly improved capacity of droplet separation, respectively. Thus, it is possible to maintain the total mass or volume flow of the air stream while significantly increasing the cooling and humidifying efficiency. The increased efficiency is specially pronounced for relatively thin pads and relatively high air velocities. Alternatively, it is possible to use a thinner pad to achieve the same cooling and humidifying effect.
Also, the new pad will have an increased strength, in particular bending resistance, which is important when handling the pad during manufacture and transport. The increased strength is primarily a consequence of the fact that there will be more points of glue contact between the corrugations of the sheets in a given volume.
Another advantage with the new structure of the air treatment pad is its light blocking capacity. Because of the oblique positioning of the air-flow channels, any light impinging onto one side of the pad will not pass through to the other side, unless the light rays are reflected at the channel walls. By proper treatment of these walls, the light reflection can be practically eliminated. So, there will be hardly any light passing through the pad. In some applications, such as in chicken farms, this feature may be very important, especially when using artificial light which is not synchronous with the daylight. In such installations, the cooling and humidifying pads are normally mounted as wall elements in the building (fans being mounted in an opposite wall).
It is also possible to use the new pad as a filter for small particles or liquid drops following the air stream, e.g. in connection with ventilation of spray booths or the like.
The light or particle blocking capacity can be significantly increased by including at least two sections of the pad located one after the other in the air stream, the channels in neighbouring sections extending sideways in opposite directions.
In order to secure a good operation also at the side edge portions of the pad, the latter may be provided with channels extending in planes aligned with said normal direction and communicating with associated obliquely sideways oriented channels disposed in a region located between these edge portions. Such edge portions are preferably wedge-like.
The pad or pads may be arranged in various ways in relation to the air stream, either with the normal direction being substantially aligned with an axial main direction of the air treatment unit or with the normal direction standing at an oblique angle to such an axial main direction. Alternatively, the air treatment unit may be provided with two or more air inlet regions each having a specific inlet flow direction. In the latter case, it is advantageous to arrange two or more pads next to each other in a zig-zag configuration in each inlet region.